The present invention generally relates to a high temperature centrifugal pump, and more particularly relates, in a first aspect thereof, to a pump having a drive shaft with a non-linear fluid channel designed to reduce the rate of fluid flow between the pump housing and the seal housing. In a second aspect thereof, the present invention relates to a thermally expandable drive shaft having a variable diameter designed to balance and compensate for different amounts of thermal expansion along its length. In yet a third aspect, the present invention relates to a tube heat exchanger operable to re-circulate and cool fluid through the seal housing interior cavity.
The present invention provides improvements to the invention of commonly owned U.S. Pat. No. 5,624,245, the entire disclosure of which is incorporated herein by reference. Centrifugal pumps which operate at high temperatures (e.g., up to about and exceeding 400° F.) typically incorporate features designed to protect the motor and seals from the high temperature of the working fluid in the pump housing. FIG. 1 of the '245 patent is reproduced herein and is seen to include a pump housing 16 connected to a pump adapter casing which surrounds a seal housing 34 containing a mechanical seal 42 which prevents fluid from passing along drive shaft 28 toward the motor and fan 56. The drive shaft connects to an impeller 22 in pump housing 16 for directing fluid from pump inlet 24 to pump outlet 26. Thermal insulators 46 are mounted about the drive shaft between the pump housing and the seal housing to reduce heat transfer from the pump housing to the seal housing. An annular passage 54 allows working fluid to travel from the pump housing to the interior cavity of the seal housing to lubricate the seal during pump operation. To aid in dissipating heat from fluid within reservoir 40, the seal housing 34 includes external and internal fins 36, 38, respectively, to help draw heat away from the reservoir and into the interior cavity 62 of the pump adapter casing 12. The interior cavity 62 is vented to the ambient through one or more holes 64 to allow the escape of heated air.
While the invention of the '245 patent is effective at providing a good degree of thermal protection to the mechanical seal, some heat still reaches the mechanical seal due to the necessary lubricating fluid delivered via passage 54. Although, as noted in the '245 patent, little liquid circulates through passage 54 after pump startup (see Col. 3, Lns. 61-67), the liquid coming from the pump housing is very hot and it would therefore be desirable to further minimize and/or reduce the velocity of the free fluid transfer between the pump housing and seal housing as much as possible. It would furthermore be desirable to carry away a higher percentage of heat from seal reservoir 40 to further protect the mechanical seal from heat damage.